Researchers study eco-roof and solar panel combinations Solar Oregon

Eco-roofing is becoming increasingly popular, especially in Portland, where the “green” movement is alive and well. These self-sustaining systems are designed to grow year-round, using whatever sunlight and rainwater they can get from the rooftops.

By Anna Snook

Vanguard

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Atop the construction mess that is Portland State’s Science Building 2, a veritable ecosystem is flourishing. Right on the rooftop, sage, thyme and succulent plants sit in raised beds—these little urban gardens are called eco-roofs.

Eco-roofing is becoming increasingly popular, especially in Portland, where the “green” movement is alive and well. These self-sustaining systems are designed to grow year-round, using whatever sunlight and rainwater they can get from the rooftops.

The so-called “green roofs” have many different functions. For many urban-dwellers, they serve as a green space that might not be readily available otherwise. In addition, they add insulation to buildings and cool down the urban environment. Green roofs also impact water-flow and storm-water runoff by absorbing much of it, and then releasing it back into the air through evaporation.

The plants in the eco-roofs absorb carbon dioxide, bring a measure of oxygen back into the cycle, capture air pollution and provide a habitat for insects and birds.

With the support from PSU, chemistry professor Carl Wamser—along with Todd Rosenstial, an assistant professor in the biology department, and David Sailor, a professor in the mechanical and materials engineering department—received a $300,000 grant from the National Science Foundation to begin testing the effectiveness of eco-roofing and solar panel combinations on Science Building 2.

Additional support comes from Portland General Electric, the Portland Bureau of Environmental Services and the Oregon Built Environment and Sustainable Technologies Center.

In general, solar panels generate more energy at cooler temperatures. However, though Portland’s perennial rainy weather seems advantageous in that respect, even this city has its share of hot weather. During summer days when temperatures soar, the surfaces of building rooftops retain so much heat that the capacity of the solar arrays is significantly decreased.

The suggestion to combine a green roof system with a solar array comes from the need to lower the rooftop temperature and thereby increase solar efficiency. Eco-roofs retain rainwater and morning dew, which generally keeps the roof cooler.

“They just need a cooler environment,” Wamser said. The researchers have tested combinations with white reflective roofing, but the added benefits of the eco-roofs make them a more efficient choice. In turn, the solar panels provide much-needed shade to the eco-roof plants, adding to the cooling effect.

“We’ve created an ecosystem here,” Wamser said. “We started with just a few succulent plants.”

Succulents are naturally drought-resistant and can survive long periods with little or no moisture. This makes them ideal for the urban rooftop ecosystem, which will ultimately take care of itself.

Researchers are still monitoring the effects of the eco-roofs to determine what else can be gained by implementing more of them. Now, a year into the project, the testing facility and monitoring systems are set up on Science Building 2.

Each part of the eco-roof is being monitored for temperature range, soil moisture levels and water flow, as well as photosynthetic activity. Researchers in the biology department also determined the best plant and soil choices for the roof, in terms of sustainability.

In addition, the researchers are measuring plant growth and carbon dioxide intake of the eco-roof systems. In a small way, these roofs can impact urban CO2 levels.

Commenting on the solar energy levels, grad student Keith James said, “We’re at about 1,232 kilowatt hours—we’ve gotten pretty close to the max rating.” He and other students have been helping monitor the test combinations.

The project’s initial goal was to monitor such results for three years, according to Wamser. However, he hopes that the facility will be running for longer than that.

“The biggest thing we hope to accomplish,” he said. “Is to show that you can do both [solar panels and eco-roofs] and that they’ll work very well—better than individually.”

Though the project is still in its early states, the data gathered could significantly impact ecological roofing choices for many in the future.

Though major funding for the project comes from the National Science Foundation’s $300,000 grant, additional support comes from a variety of other sources.